1. Field of the Invention
The present invention relates to a pneumatic tire in which a crack is prevented from being generated in an inner peripheral surface of the tire, and to a producing method of the pneumatic tire.
2. Description of the Related Art
Generally, an inner liner member which becomes an inner liner layer of a pneumatic tire is formed by rolling an unvulcanized rubber composite into predetermined width and thickness using a calender, cutting the obtained sheet-like unvulcanized rubber composite into necessary length, and winding the same around an outer periphery of a forming drum. According to this method, it is possible to handle tires of various sizes by changing the rolling width of the calender appropriately, but there is a problem that if the calender is used, the producing equipment is increased in size.
Hence, it can be conceived that an extruder is used instead of the calender, and the sheet-like unvulcanized rubber composite is extruded with a width corresponding to a tire size. In such a case, however, the die shape becomes extremely flat, a discharge pressure of rubber at its central portion becomes higher than pressures at both edges thereof and thus, there is a problem that the central portion of the unvulcanized rubber composite is extruded faster than the both edges, and cracks are produced in both edges which receive tensile force. Further, since it is necessary to prepare a die corresponding to each tire size and use the same appropriately, the number of parts is increased, and the operation becomes complicated due to exchanging operation of the die.
As disclosed in a Japanese Patent Application Laid-open No. 2002-178415, for example, it is known that a rubber ribbon having small width and thickness made of unvulcanized rubber composite is spirally wound along a circumferential direction a plurality of times to form an inner liner member. According to the ribbon winding technique, it is possible to precisely and easily form a desired cross section shape. When a pneumatic tire is produced using an inner liner member formed by the ribbon winding technique, however, it was found that there was a problem that a crack is easily generated from the ribbon interface formed in the tire inner peripheral surface, and the endurance of the tire is deteriorated. Especially in the case of a pneumatic tire having tire cross section height of less than 110 mm and a small aspect ratio (tire cross section height/tire cross section width), large distortion is applied in a region extending from the vicinity of the end of the belt layer to the tire cross section maximum width position during running, a crack generated in the inner peripheral surface in such a region was outstanding.
A Japanese Patent Application Laid-open No. 2002-160508 discloses a pneumatic tire in which an inner liner member is formed by the ribbon winding technique, and an insulation rubber extending from the vicinity of the end of the belt layer to the tire cross section maximum width position is disposed between the inner liner member and a carcass ply. According to this pneumatic tire, however, since the ribbon interface is uniformly formed in the tire inner peripheral surface, the problem of a crack in the inner peripheral surface can not be solved.
A Japanese Patent Application Laid-open No. 2002-79590 discloses a method for forming a tire inner peripheral surface of the inner liner member by a surface layer formed by winding a rubber ribbon whose width is less than 40 mm with a predetermined superposed width. According to this method, however, the relatively narrow rubber ribbon must be used, and the tire inner peripheral surface is appropriately formed with the rubber ribbon, and a crack can not be prevented from being generated in the inner peripheral surface.
A Japanese Patent Application Laid-open No. 2000-94542 discloses a method in which rubber ribbons are wound around both edges of an integrally extruded rubber extrudate to form an inner liner member. However, with respect to a problem of a crack in the inner peripheral surface, it is very important to reduce the ribbon interface in the inner peripheral surface of the region where large distortion is applied, but this method is for reducing the number of winding steps of the rubber ribbon to enhance the productivity by using the rubber extrudate, this patent document does not disclose the solving means of the problem.
A Japanese Patent Application Laid-open No. H9-29858 discloses a method in which a rubber ribbon extruded with a width of 50 to 300 mm is spirally wound along the circumferential direction to form the inner liner member. According to this method, however, it is necessary to cut unnecessary portions of a winding-start end and a winding-completion terminal end, and this is not preferable in terms of operability and cost. It is also possible to wind the rubber ribbon such that a portion which must be cut is not formed, but when a relatively wide rubber ribbon is used, superposed portions 25 of a ribbon R or a gap 26 shown in FIG. 7 are unevenly formed in the vicinity of the winding-start end or the winding-completion terminal end and thus, there is a problem that the weight balance is deteriorated.